PROJECT SUMMARY/ABSTRACT This application is being submitted in response to NOT-DA-20-047. Injection drug use has contributed to new HIV outbreaks in many regions of the United States. The parent K01 award seeks to improve the delivery of antiretroviral pre-exposure prophylaxis (PrEP) to people who inject drugs (PWID) through syringe service programs (SSPs), which provide essential HIV prevention services to this population. Large-scale public health emergencies, as well as the measures undertaken to mitigate them, can increase HIV risk among PWID (e.g., by impacting drug market characteristics and drug-related and sexual risk behaviors) while also impacting the delivery of essential prevention services. This administrative supplement proposes longitudinal, mixed methods data collection to understand the impacts of the 2019 Novel Coronavirus (2019-nCoV or COVID-19) on HIV- related risk among PWID and SSPs? capabilities to provide PrEP and other HIV prevention services over the course of the pandemic. Due to restrictions on in-person research encounters in the context of infectious disease transmission, over the course of six months, we propose virtual (video-conference) qualitative interviews with 40 PWID and 20 SSP staff as well as modified, weekly quantitative ecological momentary assessment (EMA) with participating SSPs to understand evolutions in PWID risk behaviors (Aim 1), SSP organizational functioning and staff wellbeing (Aim 2), and EMA feasibility and SSP service provision in the context of a large-scale emergency (Aim 3). Guided by the socio-ecological model, our mixed methods analyses will provide critical evidence on how to sustain the delivery of PrEP and other essential HIV prevention services to at-risk PWID during large-scale public health emergencies. Our primary innovations are the longitudinal examination of individual and organizational responses to the COVID-19 pandemic over time, the use of virtual data collection methods (including EMA with SSPs) that leverage the parent K01 award?s network of community research collaborations, and the mixed methods approach to eliciting multiple stakeholder perspectives on the impacts of this unprecedented pandemic on HIV prevention with a vulnerable substance-using population. Findings from this supplement will inform efforts to promote sustained HIV prevention service delivery during future public health emergencies while also enhancing the success of the parent K01 award focused on SSP-based implementation of PrEP for HIV prevention in a highly socially marginalized population.